The present invention is directed to a vapor vent valve especially adapted for use on gasoline tank trucks to accommodate the flow of fuel vapor to or from the headspace of the tank during a fuel loading or unloading operation.
Delivery of gasoline by tank truck from the supply terminal to a service station involves two transfers of a substantial volume--several thousand gallons--of gasoline from one tank to another. In that both tanks are sealed to prevent the escape of fuel vapor, the headspace of the tank being emptied must be vented during the emptying to maintain a constant pressure in the headspace, and the headspace of the tank being filled likewise must be vented to accommodate the escape of vapor expelled from the tank by the incoming fuel.
In the past, the underground fuel storage tanks at gasoline service stations were provided with a vent pipe which simply vented the headspace of the tank directly to the atmosphere. This practice is no longer environmentally acceptable in that substantial amounts of fuel vapor were expelled through the vent as the tank was refilled, and many states and localities now require the utilization of a vapor recovery system of some type to prevent vapor expelled from the tank during the filling operation from being disbursed into the atmosphere.
One such vapor recovery system presently in use employs a so-called coaxial elbow to couple the gasoline delivery hose from the tank truck to a central drop tube which passes downwardly freely through the storage tank fill pipe into the tank interior. The drop tube passes freely through the storage tank fill pipe so that a coaxial flow passage surrounding the drop tube is present to provide a flow path for fuel vapor expelled from the tank by the incoming fuel, and this outer flow passage is connected by the coaxial coupling to a delivery hose coupled to a pipe on the truck tank which opens, via a vent valve, into the headspace of the compartment within the truck tank which is supplying fuel to the service station storage tank. With the vent valve open, the headspaces of the underground storage tank and the storage compartment in the truck tank are connected to each other and sealed from the atmosphere so that vapor expelled from the underground storage tank simply flows back into the headspace of the tank from which the incoming fuel is flowing. The same tank truck mounted vent valve and vapor delivery pipe may be utilized at the terminal when the truck tank is being filled to conduct the vapor expelled from the truck tank during the filling operation to some vapor storage facility at the terminal.
The present invention is especially directed to an improved vent valve intended for use in a vapor recovery system of the type described above.